Coupling piece for use at simultaneous earth and/or rock drilling with an upper rotary percussion device and a lower percussion device

摘要

A coupling piece for use in drilling has a first connection (2) for connecting to an upper rotary percussion device (3), and a second connection (4) for connecting to a drill tube string (5) provided with an annular drill bit (23). The coupling piece has a first chamber (11) and a second chamber (12) separated by a piston. The pressure in the first chamber (11) is used to supply a lower percussion device (8) connected to a third connection (6) associated with the coupling piece with driving medium and for displacing the lower percussion device (8) towards the ground (15). The pressure in the second chamber (12) is used to decrease the force between the lower percussion device (8) and the ground (15) when further drill string elements are added to a drill string (7) of which the lower percussion device (8) forms a part.